The present invention relates to a method of producing ferrous sulfate heptahydrate from ferrous sulfate monohydrate.
Ferrous sulfate heptahydrate is used as chromate reducer for binding harmful chromium compounds in cement or for soil preparation. Further applications of ferrous sulfate heptahydrate include its use as fertilizer, for phosphate precipitation in purification of sewage water, for conditioning of sewage slurry, or as raw material for producing iron oxide pigments.
As metal sheets are pickled in the processing of steel, large quantities of spent pickling solutions (pickling liquor) are produced that pose a hazard to the environment and are difficult to dispose in an economical manner. As a result efforts are under way to treat the pickling liquor for a meaningful recovery and further processing. U.S. Pat. No. 5,417,955, issued May 23, 1995, describes a method and device for treating a pickling liquor to produce hydrochloric acid and ferric sulfate. Ferrous chloride is hereby precipitated in the pickling liquor by mixing with sulfuric acid to produce ferrous sulfate monohydrate in a reactor. Ferrous sulfate monohydrate is subsequently oxidized and converted into ferric sulfate.
It would be desirable and advantageous to provide an improved method of producing ferrous sulfate heptahydrate from ferrous sulfate monohydrate to obviate prior art shortcomings and to allow treatment of in particular spent pickling solution generated by the steel industry.